This is sort of unofficial app, in a sense that Windows Phone 7 SDK does not allow a specific function required for Visual Voice Mail. Anyhow a hack was developed by developers at XDA, who are the makers of this app as well.
The key features of the app currently include, retrieving and syncing your voice mail, see details and listen with quick taps, delete, call, send message and save. The app is only available in french for now, yet an update with more language options is to be released soon.
– Install the app
– navigate to settings and put the server, port, login and password (check these with your provider)
– navigate to “Messagerie” and tap the right button to refresh data